My pink dogwood is 10 yrs. old and two years ago it changed over the winter from large pink flowers and large leaves to small beige flowers and small leaves. It has been in the same spot always. There's lots of flowers and leaves, but they are so small and blah now.
Decline of the tree's flowers and leaves could indicate watering issues or more serious diseases.
You will want to make carefully inspect the tree for any other signs or changes to help determine the cause.
I have listed several links to help refresh you on the care requirements and what to look for in the tree to help make a diagnosis.